mingmwang commented on code in PR #6372:
URL: https://github.com/apache/arrow-datafusion/pull/6372#discussion_r1201428445
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datafusion/core/tests/sql/subqueries.rs:
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@@ -690,3 +690,78 @@ async fn support_union_subquery() -> Result<()> {
Ok(())
}
+
+#[tokio::test]
+async fn simple_uncorrelated_scalar_subquery() -> Result<()> {
+ let ctx = create_join_context("t1_id", "t2_id", true)?;
+
+ let sql = "select (select count(*) from t1) as b";
+
+ let msg = format!("Creating logical plan for '{sql}'");
+ let dataframe = ctx.sql(sql).await.expect(&msg);
+ let plan = dataframe.into_optimized_plan()?;
+
+ let expected = vec![
+ "Projection: __scalar_sq_1.__value AS b [b:Int64;N]",
+ " SubqueryAlias: __scalar_sq_1 [__value:Int64;N]",
+ " Projection: COUNT(UInt8(1)) AS __value [__value:Int64;N]",
+ " Aggregate: groupBy=[[]], aggr=[[COUNT(UInt8(1))]]
[COUNT(UInt8(1)):Int64;N]",
+ " TableScan: t1 projection=[t1_id] [t1_id:UInt32;N]",
+ ];
+ let formatted = plan.display_indent_schema().to_string();
+ let actual: Vec<&str> = formatted.trim().lines().collect();
+ assert_eq!(
+ expected, actual,
+ "\n\nexpected:\n\n{expected:#?}\nactual:\n\n{actual:#?}\n\n"
+ );
+
+ // assert data
+ let results = execute_to_batches(&ctx, sql).await;
+ let expected = vec!["+---+", "| b |", "+---+", "| 4 |", "+---+"];
+ assert_batches_eq!(expected, &results);
+
+ Ok(())
+}
+
+#[tokio::test]
+async fn simple_uncorrelated_scalar_subquery2() -> Result<()> {
+ let ctx = create_join_context("t1_id", "t2_id", true)?;
+
+ let sql = "select (select count(*) from t1) as b, (select count(1) from
t2) as c";
Review Comment:
> I suggest also adding an error case here for a query that doesn't produce
a single row? Something like
>
> ```sql
> select (select t1_id from t1) as b, (select count(1) from t2) as c
> ```
>
> In which case I would expect an error
This query can not be de-correlated by this rule, the subquery expression is
kept and the real physical plan is not executable.
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